Method for soldering electronic component

ABSTRACT

A soldering method wherein a high-energy beam such as a laser beam is projected onto different lead terminal arrays of electronic components, the beam being projected in a scanning manner a plurality of times two-dimensionally and continuously is described. The invention further relates to a soldering apparatus comprising a mechanism for holding an electronic component by the tip thereof, a rotary drive mechanism (27) which turns the electronic component holding mechanism so that the position of the electronic component in the rotational direction is brought into agreement with a practical mounting position on the circuit board, holding unit-drive mechanisms (21, 22, 25) that move the electronic component-holding mechanism three-dimensionally, beam radiation mechanisms (41, 42) for irradiating the surface of the circuit board with high energy, beam radiation angle change mechanisms (53, 54) for changing the radiation angle of the high-energy beam emitted from the beam radiation mechanisms relative to the circuit board, and a beam scanning controller (47) which controls the beam radiation angle change mechanisms such that the high-energy beam scans a predetermined lead terminal array of the electronic components mounted on the circuit board a predetermined number of times. Using this apparatus, the soldering is effected under conditions where the temperature rise near the lead terminals and the temperature distribution are made uniform.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for solderingan electronic component of a semiconductor device, e.g., a flat packageIC to a printed circuit board.

BACKGROUND ART

Conventionally, an automatic soldering apparatus has been used formounting and soldering an electronic component 1 having lead arrays 3extending substantially horizontally from the respective sides of itsmain body portion 2 on a predetermined position on a circuit board (notshown).

One example of such soldering process presses a heater chip against thelead terminal arrays 3 of the electronic component 1 and thereafterheats the heater chip, thereby performing soldering. However, since sucha soldering process uses a physical contact, various problems, e.g., apositional error of the electronic component upon contact with theheater chip occur. In order to solve these problems, a solderingapparatus has recently been developed wherein a soldering method using anon-contact process such as a laser beam is employed.

One of the soldering apparatuses using such a non-contact process has abench for placing a circuit board on which an electronic component 1 istemporarily fixed, a laser emitting section arranged to oppose thecircuit board on the bench, and a laser moving means such as an X-Ytable on which the laser emitting means is mounted thereon for movingthe laser emitting means in the X-Y direction on the circuit board.

In the soldering process of such soldering apparatus, the laser movingmeans is driven to move the laser emitting means in the X-Y direction,so that a laser beam A sequentially radiates the lead terminal arrays 3.

There is another process for soldering in which the laser beam is usedas a linear spot, and simultaneously radiates the terminals of a leadterminal array 3 on one side of an electronic component.

However, in the conventional soldering process described above, when onelead terminal is soldered the laser beam is to be moved to the next leadterminal for serially soldering the terminals, or when one terminalarray is simultaneously soldered by using the linear type beam spot,another terminal array should be soldered continuously. Therefore, onelead terminal can be thermally influenced by an adjacent lead terminalto cause undesirable results. For example, adjacent lead terminals areconnected through solder and are electrically connected each other,thereby resulting in a solder bridge.

In addition, local temperature rise in the vicinity of the laserradiated portion enhances the above problem. This problem tends toeasily occur particularly in a narrow pitch flat package IC in which thelead pitch is for example 0.5 mm or 0.65 mm. A technique for solvingthis problem has been desired.

Further, since all the lead terminal arrays are soldered with a singlelaser beam, reduction in the soldering time is limited due to thescanning performance of the laser beam.

The present invention has been made in order to solve the drawbacks ofconventional soldering process. Since the present invention uses a highenergy beam such as a laser beam and radiates two-dimentionally andcontinuously each lead terminal array in a plurality of times, thetemperature rise rate and the temperature distribution in the vicinityof the lead terminals can be uniformed. Therefore, various problemsarising from the non-uniformed temperature rise rate and temperaturedistribution in the vicinity of the lead terminals, e.g., a solderbridge wherein adjacent lead terminals are connected through solder andare electrically conducted, can be prevented, thereby resulting in anincrease of solder operation precision.

Furthermore, the present invention uses a plurality of beams forradiating different lead terminal arrays of an electronic component,thereby greatly reducing the soldering time.

Furthermore, in the present invention soldering operation and electronicconveying/mounting operation are performed simultaneously, therebysimplifying the operation.

Furthermore, since in the present invention soldering is performed byusing a high energy beam, physical contact of an electronic componentwith a soldering apparatus during soldering can be prevented, therebyreducing a positional error in mounting.

DISCLOSURE OF INVENTION

In an electronic component soldering method of the present invention asa first embodiment, an electronic component is mounted on apredetermined position on a circuit board in accordance with apredetermined positioning information, the electronic component has apolygonal main body and lead terminal arrays on a plurality of sides ofthe main body, and a plurality of high energy beams are scanned onpredetermined positions of the lead terminal arrays of the electroniccomponent, thereby soldering the lead terminal arrays to a lead wiringpattern formed on the circuit board. The method is characterized in thatthe lead terminal arrays are grouped in a plurality of terminal groups,and the high energy beams two-dimensionally, simultaneously radiate theplurality of lead terminal groups a plurality of times, each high energybeam having an emission power insufficient for complete soldering by asingle radiation, thereby performing soldering.

An electronic component soldering apparatus of the present invention ischaracterized by comprising an electronic component holding means forholding an electronic component by the tip thereof, a rotational drivingmeans for rotating the electronic component holding means so that aposition of the electronic component in a rotating direction is alignedon a predetermined position on a circuit board, a holding sectiondriving means for three-dimensionally moving the electronic componentholding means, a beam emitting means arranged above the circuit board,for emitting a high energy beam onto a surface of the circuit board, abeam emission angle changing means for changing an emission angle of thehigh energy beam emitted from the beam emitting means to the circuitboard, and a beam scanning control means for controlling the beamemission angle changing means so that the high energy beam scans apredetermined lead terminal array of the electronic component mounted onthe circuit board in a predetermined of times.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an outer appearance of a mountingapparatus according to an embodiment of the present invention;

FIG. 2 shows an arrangement of a chucking head section shown in FIG. 1;

FIG. 3 shows the optical system of the laser emitting means and anoperation for driving the optical system;

FIG. 4 shows an example of scanning of an electronic component with alaser beam; and

FIG. 5 is a plan view of an electronic component.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 1 shows a mounting apparatus used in an embodiment of the presentinvention. A mount head section 24 is mounted on an X-Y table 23 drivenby X-axis driving means 21 and Y-axis driving means 22. A Z table 26connected to a z-axis driving means 25 is provided in the mount headsection 24. A rotational driving means 27, a chucking head 28, aconnecting shaft 29, a thread cylindrical chucking tool shaft 30, and achucking terminal 31 for chucking an electronic component are providedin one body on one side of the Z table 26. A pair of laser emittingmeans 41 for soldering electronic components and a pair of laser opticalunits 42 for guiding a laser beam through inside optical fibers areprovided on the connecting shaft 29.

The chucking terminal 31 can move three-dimensionally and can rotate bymeans of the X-Y table 23, the Z table 26, and the rotational drivingmeans 27. An apparatus mounting section 36 having a bench 33 for placinga circuit board 32 thereon, a control panel 34, an electronic equipmentsection 35 having a control mechanism, and the like are arranged on thefront of the X Y table 23.

A laser beam oscillator 43, a laser optical unit 44, and optical fibers45 are arranged behind the X-Y table 23. The laser oscillator 43oscillates, e.g., a YAG laser beam. The laser optical unit 44 guides thelaser beam emitted from the oscillator 43 into the optical fibers 45.The optical fibers 45 optically connect the optical units 42 and 44.

The laser oscillator 43 is provided with a Q switch for intermittentlyoscillating the laser beam. The laser oscillator 43 can thereforeoscillate the laser beam at a desired timing.

The mount head section 24 will be described in more detail withreference to FIGS. 2 and 3. The cylindrical connecting shaft 29 isprovided on the upper end of the thread cylindrical chucking tool shaft30 having the chucking terminal 31 on its lower end. The chucking toolshaft 30 serves as the rotating shaft to rotate the electroniccomponent 1. The pair of laser optical units 42 and the pair of laseremitting means 41 are provided on the cylindrical connecting shaft 29.Each pair diagonally sandwiches the central axis of the connecting shaft29.

First and second laser reflecting plates 51 and 52 are provided in thelaser emitting means 41, as shown in FIG. 3. The first laser reflectingplate 51 rotates about an axis of rotation "a" to scan the emitted laserbeam A on the circuit board 32. The second laser reflecting plate 52perpendicularly opposes the first laser reflecting plate 51 and rotatesabout an axis of rotation "b" perpendicular to the axis of rotation "a".

The laser reflecting plates 51 and 52 are respectively connected toreflecting plate rotating means 53 and 54 controlled by an opticalsystem control means 47 of a CPU 46 of the mounting apparatus. The laserreflecting plates 51 and 52 are rotated by the reflecting plate rotatingmeans 53 and 54 to two-dimensionally scan the laser beam on the circuitboard.

A soldering method using the soldering apparatus having the abovedescribed arrangement will be described.

The electronic component 1 previously stored in a chip tray 49 ischucked by the chucking terminal 31. A drive control means 48 drives theX-, Y , and Z-axis drive means 21, 22, and 25 in accordance with anelectronic component positioning information previously stored in theCPU 46 of the mounting apparatus to convey the electronic component 1 toa predetermined position on the circuit board 32. The electroniccomponent 1 is then aligned in the X-Y direction. The chucking toolshaft 30 is rotated by the rotational driving means 27 in a similarmanner to align the electronic component 1 in its rotating direction.The Z table 26 is driven to move the chucking terminal 31 downward,thereby mounting the electronic component 1 at the predeterminedposition on the circuit board 32.

When the mounting operation is completed in this manner, the laseroscillator 43 is driven to solder the lead terminal array 3 of theelectronic component 1 and a lead wiring pattern 50 formed on thecircuit board 32.

In this case, the laser beam A is scanned in the following manner. Whilethe optical systems of the two laser emitting means 41 diagonallyopposing each other through the axis of rotation of the electroniccomponent 1, as shown in FIG. 4, the laser beam A separately andsimultaneously scans lead terminal arrays 3a and 3b on adjacent twosides of the electronic component 1 a plurality of times in an L-shapedmanner. This scanning control is performed two dimensionally by thelaser reflecting plates 51 and 52 and the reflecting plate rotatingmeans 53 and 54 for rotating the plates 51 and 52. In this embodiment,the plates 51 and 52 perform scanning in the Y-X direction,respectively, on the circuit board 32. Since the laser beam is scannedtwo-dimensionally, it can effectively scan an electronic component whichhas a polygonal shape in order to increase the electronic componentmounting density. In other words, rotating alignment operation of acircuit board mounting an electronic component can be simplified.

Laser radiation with the laser beam A is stopped at portions of theelectronic component 1 not corresponding to the lead terminal arrays 3,i.e., four corners R of the electronic component 1, thereby preventingburning of the circuit board caused by the laser beam. The laser beam Ais enabled/disabled by a Q switch 43a provided to the laser oscillator43 for oscillating, e.g., a YAG laser beam.

In this manner, when a plurality of high energy beams such as laserbeams are used and the lead terminal arrays on the respective sides ofthe electronic component are irradiated with the different high energybeams a plurality of times, the temperature rise rate in the vicinity ofthe lead terminals can be easily kept inform, and poor soldering such asa solder bridge caused by a local temperature rise is eliminated,resulting in high-precision soldering. Since a plurality of beamsradiate different lead terminal arrays simultaneously, the solderingtime is greatly reduced.

In this embodiment, the laser beam is used as the high energy beam.However, the present invention is not limited to this. Any high energybeam other than the laser beam, e.g., a high energy infrared orultraviolet ray, that can be used for non-contact soldering, can beemployed.

As described above, according to the present invention, the temperaturerise rate in solder portions are made uniform, and high-precisionsoldering without erroneous soldering can be performed within a shortperiod of time. Since the soldering operation and the electroniccomponent conveying/mounting operation can be performed simultaneously,the entire operation can be simplified. Since soldering is performedusing a high energy beam, a physical contact between the electroniccomponent and the soldering apparatus during soldering is prevented, anderroneous mounting is eliminated, resulting in high-precision soldering.

I claim:
 1. A method for soldering lead terminals of an electroniccomponent to a lead wiring pattern formed on a circuit board, theelectronic component including a main body having a plurality of sides,the lead terminals being disposed along at least one of the plurality ofsides, the method comprising the steps of:mounting the electroniccomponent on a predetermined position on the circuit board in accordancewith predetermined positioning information to substantially juxtaposethe lead terminals of the electronic component with the lead wiringpattern of the circuit board; and scanning high energy beams, aplurality of times, along a path traversing the lead terminals of theelectronic component and the lead wiring pattern of the circuit board tosolder the lead terminals to the lead wiring pattern by directing a highenergy beam to one or more reflecting plates and rotating the reflectingplates to scan the beam a plurality of times along the path, the step ofscanning high energy beams being effectuated simultaneously using aplurality of high energy beams to scan a plurality of groups of saidlead terminals.
 2. The method according to claim 1, wherein the step ofscanning of said high energy beams is stopped between adjacent sides ofsaid electronic component.
 3. The method according to claim 1, whereinthe high energy beams are laser beams.